Android: Order Id Of The Purchased App

We are planning to move from a paid app to a free one with in app purchase. We need to give any user, who paid for the app, get the in app purchase for free. I am thinking of the

Solution 1:

Getting email address will need you to modify your existing Paid app. Also it's not recommended for above approach ( + cases where users have multiple accounts in same phone and doesn't remember which email is used will create more issues)

I would recommend to use https://developer.android.com/guide/topics/manifest/manifest-element.html#uid

android:sharedUserId

The name of a Linux user ID that will be shared with other applications. By default, Android assigns each application its own unique user ID. However, if this attribute is set to the same value for two or more applications, they will all share the same ID — provided that they are also signed by the same certificate. Application with the same user ID can access each other's data and, if desired, run in the same process.

Define same userId across paid app and new FREE app with in-app purchases. Certain data within paid app can be used to identify the user without asking any more input from users.

Take a look at one of solution provided in this answer by user caw Offering additional media resources (graphics/sounds) as Google Play in-app billed items